Plasmon-Enhanced Infrared Emission Approaching the Theoretical Limit of Radiative Cooling Ability

Abstract

Radiative cooling, a passive cooling technique, has shown great potentials in recent years to lower the power consumption of air conditioning. With the ever-increasing cooling power being reported, the theoretical cooling limit of such a technique is still unclear. In this work, we proposed a theoretical limit imposing an upper bound for the attainable cooling power. To approach this limit, we exploited the localized surface plasmon resonance (LSPR) of self-doped In 2 O 3 nanoparticles, which enhance the emissivity in both primary and secondary atmospheric windows. The measured cooling power of poly(methyl methacrylate) (PMMA) films containing 4.5% In 2 O 3 nanoparticles is very close to the limit with the closest value only about 0.4 W/m 2 below the limit. Hopefully, this work may help the researchers better evaluating the performance of their device in the future and pave the way for achieving even higher radiative cooling powers during the daytime operations with the help of LSPR.

Reconfigurable and Renewable Nano‐Micro‐Structured Plastics for Radiative Cooling

“…For an ideal atmospheric ambient with super dry air and 1% humidity, the first atmospheric spectral window (8–13 µm) and the second atmospheric window (16–25 µm) show the maximum transparency. [ 41 ] The ambient temperature of 300 K and h non‐radiative of 0, 3, and 8 W m −2 K −1 are taken as examples, where h non‐radiative of 0 indicates an ideal thermal insulation case, h non‐radiative of 3 and 8 W m −2 K −1 indicate different parasitic heat loss cases. On the basis of the theoretical model, we can predict the temperature drops of the nano‐micro‐structured plastic in the nighttime and daytime.…”

Colorful surfaces for radiative cooling

“…Therefore, this type of colored radiative cooling materials requires an even more stringent spectral selectivity than white cooling materials. [80][81][82][83][84][85][86][87][88][89][90] On the other hand, due to this inevitable optical absorption, the cooling power of these colored absorbing surfaces is generally lower than that obtained by white materials. Next, we will discuss another strategy to enable colorful radiative cooling surfaces with structural colors.…”

Accurately Quantifying Clear-Sky Radiative Cooling Potentials: A Temperature Correction to the Transmittance-Based Approximation

“…Models that yield the level of detail needed for such calculations are comparatively rare [1,5,13]. One model, which has achieved almost universal use in recent radiative cooling literature, is the transmittance-based cosine approximation [1,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29], which was first used as part of a more comprehensive model by Granqvist in 1981 [1]. This model assumes that the irradiance of the atmosphere originates from greenhouse gases, including water vapor, carbon dioxide and ozone, and calculates the spectral, angular sky irradiance based on an effective spectral angular emittance as follows:…”

“…Since the irradiance from ozone and absorptance/emittance of SiO films have little overlap and the SiO film has a narrowband emittance, such a choice is justifiable in that context. However, the approximation has since been used to calculate the radiative cooling potentials of ideal emitters and cooling powers of radiative coolers with different spectral emittances, leading to both a systematic underestimation of cooling potential and a related overestimation of performance [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. The MODTRAN hemispherical emittance, which is more accurate, should ideally be used instead.…”